Parastoo, meaning swallow bird in Farsi, urged those it listed to sign a petition calling for an IAEA investigation into what it claims as Israel's undeclared "nuclear arsenal". The Jewish state is widely believed to have nuclear weapons but has neither confirmed nor denied this under a "strategic ambiguity" policy.

The names published included physicists at US, British and Japanese universities as well as researchers from Japan Atomic Agency, the US government's Los Alamos National Laboratory and Russia's Space Research Institute. The information published is not thought to be anything in relation to confidential work carried out by the IAEA.

The agency has been investigating Iran which it says is developing nuclear weapons at its uranium facility- a claim which the country vehemently denies. In a report, it said it could not be certain that all nuclear material in Iran was for peaceful activities.

Gill Tudor, a spokesperson for the agency, apologised for the breach saying the IAEA "deeply regrets this publication of information stolen from an old server".

She insisted that the server was shut down "some time ago" and experts were already working on removing any security risks before it was hacked yesterday.

"The IAEA's technical and security teams are continuing to analyse the situation and do everything possible to help ensure that no further information is vulnerable," she added.